In many applications requiring a high degree of accuracy and reliability, such as high precision measurements or high precision treatments within the fields of fine mechanical, surveying or medical applications, it is often important to be able to securely or firmly lock shafts or spindles without any movement, e.g. translational, or rotation or turning of the shafts during the locking procedure. That is, it is important to achieve a tension less fixation of the shafts. Furthermore, it is also important in such applications to be able to firmly lock the shafts with a sufficient force to ensure that a secure and reliable locking of the shafts is achieved. Thereby, the locked position can be maintained over time until locked up to release the shafts from the fixation. One specific application with such requirements is within the field of radiation technology and, in particular, in a fixation device for immobilizing a head of a patient relative a treatment unit during treatment of the head.
The development of surgical techniques have made great progress over the years. For instance, for patients requiring brain surgery, non-invasive surgery is now available which is afflicted with very little trauma to the patient.
Stereotactic radiation surgery is such a minimally invasive treatment modality that allows delivery of a large single dose of radiation to a specific intracranial target while sparing surrounding tissue. Unlike conventional fractionated radiation therapy, stereotactic radiation surgery does not rely on, or exploit, the higher radiation sensitivity of neoplastic lesions relative to normal brain (therapeutic ratio). Its selective destruction depends primarily on sharply focused high-dose radiation and a steep dose gradient away from the defined target. The biological effect is irreparable cellular damage and delayed vascular occlusion within the high-dose target volume. Because a therapeutic ratio is not required, traditionally radiation resistant lesions can be treated. Because destructive doses are used, however, any normal structure included in the target volume is subject to damage.
One such non-invasive radiation therapy technique is so called LINAC (Linear Accelerator) radio therapy or radiation therapy. In a LINAC radiation therapy system, a collimated x-ray beam of a very high energy level is focused on a stereotactically identified intracranial target.
Another system for non-invasive surgery is sold under the name of Leksell Gamma Knife®, which provides such surgery by means of gamma radiation. The radiation is emitted from a large number of fixed radioactive sources and are focused by means of collimators, i.e. passages or channels for obtaining a beam of limited cross section, towards a defined target or treatment volume. Such a radiation device is, for example, referred to and described in U.S. Pat. No. 4,780,898.
In radiation therapy system, the head of a patient is immobilized in a stereotactic instrument which defines the location of the treatment volume in the head. Further, the patient is secured in a patient positioning unit which moves the entire patient so as to position the treatment volume in coincidence with the focus point of the radiation unit of the radiation therapy system. Consequently, in radiation therapy systems, such as a LINAC system or a Leksell Gamma Knife® system, it is of a high importance that the positioning unit which moves the patient so as to position the treatment volume in coincidence with the focus point of the radiation unit of the system is accurate and reliable. That is, the positioning unit must be capable of position the treatment volume in coincidence with the focus point at a very high precision. This high precision must also be maintained over time.
Hence, in order to obtain as favourable clinical effect as possible during the therapy is it of an utmost importance that the radiation reaches and hits the target, i.e. the treatment volume, with a high precision and thereby spares the healthy tissue being adjacent to and/or surrounding the treatment volume. To achieve this, the patient must be immobilized during a therapy session and, moreover, the position of the head of the patient must be the same in a therapy session as in a reference position, i.e. the position during the session when the pictures to create the therapy plan were captured by means of, for example, Computerized Tomography Imaging (CT-imaging). In fractionated radiation therapy where the patient is docked in and out of the radiation therapy system at each therapy session, it must thus be secured that the patient is positioned in exact the same way as in the session when the pictures were captured to create the therapy plan.
One prior art method for enabling measurements of the head of a patient and for immobilizing or fixating the head of the patient during neurological diagnosis, therapy or surgery, in particular during radiation therapy relatively an interface unit, frame or adaptor adapted to be fixated to a radiation therapy unit is a stereotactic frame provided with pin support members in form of posts having fixation pins for invasive fixation to the skull of a patient. In use during therapy or diagnostics, the stereotactic frame is arranged around the head of a patient, and the fixation pins of the posts connected to the frame are screwed into or to abutment against the bone of the skull, thus ensuring a rigid fixation of the reference system. The frame is then rigidly held in position in relation to a patient table. This kind of frame is obviously not suitable for so called fractionated therapy.
Thus, there is a need within the art of radio therapy systems for head fixation arrangements and locking devices for such head fixation arrangements that enable an accurate and repeatable fixation of a head of a patient relative a radiation therapy unit during neurological diagnosis, therapy or surgery, to secure that the patient, or more specifically the head of the patient, is positioned in exact alignment to a reference position or at a known position in relation to the reference position, and that this done every single therapy occasion of the fractionated therapy.